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Are you talking about the manual passcode that you assign on each console? Or the password to his XBox Live account?
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What do I do if I forget my pass code for my Xbox LIVE Account?
If you have forgotten your Xbox LIVE account pass code, recover your account using Xbox LIVE.

To recover a gamertag

To recover your gamertag, you need the associated Windows Live ID and password for your Xbox LIVE account.

If you're signed into Xbox LIVE with another gamertag, press the Guide button, and then press X on your controller to sign out.

Press the Guide button again, and select Recover Gamertag.

Select Recover Gamertag again.

Enter your Windows Live ID and password for the gamer profile that you want to recover.

it only means that your gamer profile is corrupted here's how to recover and delete your gamer profile

to delete the gamer profile

1.press the guide button or the silver button in the middle of the controller2.go to settings blade3.select system settings4.select memory5.select hard drive6.select game profile choose your profile and choose delete profile only

to recover the gamertag

1.make sure you are connected to the internet2.logout/sign out other profiles in the console3.press the guide button or the silver button in the middle of the controller4.chose recover gamertag5.enter the gamertag6.enter the email and password ( email or windows live ID this is the email you use for the sign up of the gamertag)

If you have forgotten your pass code, and if you have to remove it to sign into Xbox LIVE, follow these steps:

Note The following steps apply only to Xbox LIVE online profiles. When you delete an offline
profile, you lose any Gamerscore that is associated with the profile.
You also lose achievements and statistics that are associated with the
profile.

Delete the profile for which you forgot the pass code. To delete a profile, follow these steps:

In the My Xbox area, select System Settings.

Select Memory.

Select the memory device on which your profile is stored.

Select Gamer Profiles.

Select the profile that you want to delete.

Select Delete. When you are prompted, select Delete Profile Only.

In the Xbox LIVE section of the Xbox Dashboard, select Recover Gamertag from Xbox Live.

Select Yes when you receive the following message:
To join Xbox LIVE, you must exit your current session.

Enter the gamertag for which you want to remove the pass code, and then select Done.

Select Next.

In the E-mail Address
section, type the Windows Live ID credentials (the e-mail address and
password that you use to sign in to the Windows Live ID) that are
associated with your gamertag, and then select Done.

Enter the password for the Windows Live ID account, and then select Done.

Select Sign In.

If you want to set the pass code again, follow the steps to set an Xbox LIVE pass code.